ive followed it as closely as i could. there are a few things that im not entirely sure about, such as what the difference between the TRIG and the BD inputs to the circuit perhaps someone could clear that up.
also there is a cap marked c?, this is the cap that runs to GND on the far right of the schematic after Q44 i dont know what its value is although it says 22 on it (not sure if theres a digit missing here)
****edit : this cap is C48 and is 220p****
the cap marked c5? is marked as i dont know the actual part number for this, im assuming from the schematic that its a 1uf/50v cap but thats just my guess.
****edit : the value is correct and its C50****
ive taken B2 as +v as this seems to make the most sense, cannot find references to B2 anywhere else and the opamp has B2 as the +v input.

Q40 is PNP 2SA733 all others are NPN 2Sc945 the op amp is a jrc4558 although it matches the pinout of a TL series opamp so one of these may(or may not) work

ive probably missed a boatload of info out, so ask away (im really not very good at all this but i might be able to help)

x,y,z are jumpers as its a single sided layout, i didnt really think about the position of them until too late. the power caps are rough values, use your favourites.
off to etch this and try it out myself

-bubzyLast edited by bubzy on Sat Aug 13, 2011 2:12 am; edited 1 time in total

Wow, thats a real nice project over there. so many things to make me doubt the reason i even made this pcb in the first place :s
Ill stick at it for a while and see if i can manage a functional bass drum module. thanks for the link, some really useful information there!

so forgive me if im being an idiot. but it seems possible that the BD input is the accent input and this can be a voltage divider to change the "accentuation" of the sound output while the other input is just a normal trigger in for the circuit?

so forgive me if im being an idiot. but it seems possible that the BD input is the accent input and this can be a voltage divider to change the "accentuation" of the sound output while the other input is just a normal trigger in for the circuit?

Hi Fonik:
If you going to layout some 808 sounds, take in account that there are some errors in the original schematics. There is good info at the eight-oh-eight site about them.
For example I couldn't get the clap sounding right, then I read there, that there is an electrolitic cap that is reversed in the original schematic (and in the microLARGE PCB too), I reversed it, and the clap start to sound right.
Also there are corrections to the noise circuit (they appear in the service manual but not in the schematic), and some other things.

If you want to feed the bass drum variable voltage triggers of appropriate width you can just leave out Q39 and Q40 and insert the trigger into where the collector of Q40 would go. Then you can use a midi to trigger converter with velocity sensitive trigger outputs or a sequencer with variable trigger outputs.

Hi Fonik:
If you going to layout some 808 sounds, take in account that there are some errors in the original schematics. There is good info at the eight-oh-eight site about them.
For example I couldn't get the clap sounding right, then I read there, that there is an electrolitic cap that is reversed in the original schematic (and in the microLARGE PCB too), I reversed it, and the clap start to sound right.
Also there are corrections to the noise circuit (they appear in the service manual but not in the schematic), and some other things.

- White noise level: I didn't liked so much, and I was short of space in the front panel.
- Clap Offset: Idem. As a side note the clap offset of the 909 clap is much more interesting.
- Clap reverb amount: I didn't implemented, but I think it will be a great addition if I find a spot in the frontpanel.
- Cowbell tunning: I did it, but I found very difficult to tune the original sound of the cowbell, hihhats and cymbal, so I use a switch to to select between the pots and 2 trimmers calibrated as said in the original manual.
- White & Pink Noise & Schmitt Triggers input: I dind't implemented, but I'm thinking of it, specially the Schmitt trigger one.
- Self Oscilation of Congas: I didn't liked at all, it was unusefull to me. I limited the decay time with a resistor to avoid it. This resistors are only in use when in conga mode, so they don't affect the toms.

Another mods I didn't liked or not implemented:

- Bass Drum Xtra Decay: I have implemented, but I barely use it, because it almost don't have effect until the self oscillation start, and I don't like when in self oscillation.
- Clap Filter: I didn't liked at first, when the clap was working bad, so I just use a trimmer to set it to my taste, but when the clap start to work well, and I re-calibrated, I missed the option to have it on the frontpanel.

Right now I have some issues:
The clap reverb sometimes didn't trigger.
The clave don't sound like the 808 clave at all.
The MIDI interface is a little bit slow (I used a modded MIDIbox CV), the accents sometimes are a little behind the trigger, so the accent is randomly skipped. That's why I'm building the MSC175 MIDI interface, plus it have velocity for every sound._________________Sebo
---------------------------------------
My Music:
www.cosaquitosenglobo.com.arwww.myspace.com/cosaquitosenglobo

- Cowbell tunning: I did it, but I found very difficult to tune the original sound of the cowbell, hihhats and cymbal, so I use a switch to to select between the pots and 2 trimmers calibrated as said in the original manual.

Not a bad idea! I'm not so concerned about having it exactly the same as the original. Besides, I can tune it close enough by ear.

I didn't know about 808's clap reverb didn't trigger always. I have a friend that have an original 808, I will listen to it.

The tuning of the Schmitt Trigger affects High Hats and Cymbal, and is very hard to tune it like the original hats/cymbal. And the hats/cymbal sounds great with the original tunning, remember that the 6 frequencies of the schmitt trigger interacts in a very unique way. Cowbell is easier to tune (you hear only 2 frequencies).

The filter of the hats are great for some build up filter thing, but I mostly use them as an EQ.
The filter of the Rimshot is nice, if you set it low, gets closer to a 909 rimshot, but I use it more of the time close to the original setting.
When I set it to clave the filtering is a lot of fun, specially when retuning the oscillators, but, as I said, my clave didn't sound like an 808 clave.
The filter of the maraca is like the Hats, but I use it very up all the time, I like very high filtered maracas.

The Tune and Tune Envelope mods of the Bassdrum are totally great. You can get really punchy BDs.

If you going to layout some 808 sounds, take in account that there are some errors in the original schematics. There is good info at the eight-oh-eight site about them.
For example I couldn't get the clap sounding right, then I read there, that there is an electrolitic cap that is reversed in the original schematic (and in the microLARGE PCB too), I reversed it, and the clap start to sound right.
Also there are corrections to the noise circuit (they appear in the service manual but not in the schematic), and some other things.

Sebo,
Do you have info about which cap is reversed on the schematic? I got a PCB for Eric Archer's Clap Raca and I cannot get it to sound like the 808 clap. It's based off of the 808/909 (more closely, the 909) circuit with some mods and a power supply circuit plus trigger input. The clap consists of a four-attack envelope, but I can't get the four peaks, just one attack. I've tried tweaking a few component values, but to no avail. And now the eight-oh-eight site you referred to is completely gone. Please help!

Hmm.... I had trouble accessing the 808 site too. Do you think that in the light of the recent analogue direction from Korg (monotron and tribe), that Roland may be working the analogue wonder again and are stomping out competition?

So I reversed the cap and got a brief moment of the familiar clap sound, albeit with hum, but when I wiggled the wires while turning the pots, it degenerated to a low frequency, saw wave burst. It sounds worse than ever, so I think I may have fried an IC or something. Anyone know of a self-contained (with power supply circuit) handclap project out there? The one I tried was a prototype with no guarantees. I'm also looking for a rimshot unit.

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